Problem: Expand.
We expand the parentheses using the distributive property : $ A(B+C)= A\cdot B+ A\cdot C$ We can also think about the problem using an area model: $r^2$ $-2$ $8r^2$ Here's how the solution goes, algebraically: $\begin{aligned} &\phantom{=}{8r^2}(r^2-2) \\\\ &={8r^2}(r^2)+{8r^2}(-2) \\\\ &=8r^4-16r^2 \end{aligned}$ Here's how the solution looks in terms of the area model: $8r^4$ $-16r^2$ $r^2$ $-2$ $8r^2$ In conclusion, $8r^2(r^2-2)=8r^4-16r^2$